 window.onload = function(){
        strYYYY = document.form1.YYYY.outerHTML;
        strMM = document.form1.MM.outerHTML;
        strDD = document.form1.DD.outerHTML;
        MonHead = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];

//先给年下拉框赋内容
        var y = new Date().getFullYear();
        var str = strYYYY.substring(0, strYYYY.length - 9);
        for (var i = (y-30); i < (y+30); i++) //以今年为准，前30年，后30年
        {
            str +="<option value='"+ i +"'>"+ i +"</option>rn";
        }
        document.form1.YYYY.outerHTML = str +"</select>";

//赋月份的下拉框
        var str = strMM.substring(0, strMM.length - 9);
        for (var i = 1; i < 13; i++)
        {
            str +="<option value='"+ i +"'>"+ i +"</option>rn";
        }
        document.form1.MM.outerHTML = str +"</select>";

        document.form1.YYYY.value = y;
        document.form1.MM.value = new Date().getMonth() + 1;
        var n = MonHead[new Date().getMonth()];
        if (new Date().getMonth() ==1 && IsPinYear(YYYYvalue)) n++;
        writeDay(n); //赋日期下拉框
        document.form1.DD.value = new Date().getDate();
    }
    function YYYYMM(str) //年发生变化时日期发生变化(主要是判断闰平年)
    {
        var MMvalue = document.form1.MM.options[document.form1.MM.selectedIndex].value;
        if (MMvalue ==""){DD.outerHTML = strDD; return;}
        var n = MonHead[MMvalue - 1];
        if (MMvalue ==2 && IsPinYear(str)) n++;
        writeDay(n)
    }
    function MMDD(str) //月发生变化时日期联动
    {
        var YYYYvalue = document.form1.YYYY.options[document.form1.YYYY.selectedIndex].value;
        if (str ==""){DD.outerHTML = strDD; return;}
        var n = MonHead[str - 1];
        if (str ==2 && IsPinYear(YYYYvalue)) n++;
        writeDay(n)
    }
    function writeDay(n) //据条件写日期的下拉框
    {
        var s = strDD.substring(0, strDD.length - 9);
        for (var i=1; i<(n+1); i++)
            s +="<option value='"+ i +"'>"+ i +"</option>rn";
        document.form1.DD.outerHTML = s +"</select>";
    }
    function IsPinYear(year)//判断是否闰平年
    { return(0 == year%4 && (year%100 !=0 || year%400 == 0))}
    function optionsClear(e)
    {
        e.options.length = 1;
    }
    
